In case SAC 2021:66, the Finnish Supreme Administrative Court held that the cost-plus method was the most suitable method in a setting where a Finnish parent company provided centralized financing to its foreign subsidiaries. This article analyses how the Court’s approach and the outcome of the case align with the OECD Transfer Pricing Guidelines and with the Court’s earlier case law on group internal financing. It also discusses the problems that may arise if the courts, instead of practical and tailor-made reasoning, give the text of the OECD Guidelines a law-like role.